DevTools: Use JS symbols instead of strings for eligible events.

third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @constructor
  * @extends {WebInspector.VBox}
  * @param {!WebInspector.TimelineModel} model
  * @param {!Array<!WebInspector.TimelineModel.Filter>} filters
  */
@@ skipping 827 matching lines @@
     var columns = [
         {id: "total", title: WebInspector.UIString("Total Time"), fixedWidth: true, width: "110px"},
         {id: "activity", title: WebInspector.UIString("Activity")}
     ];
     this._dataGrid = new WebInspector.ViewportDataGrid(columns);
     this._dataGrid.setResizeMethod(WebInspector.DataGrid.ResizeMethod.Last);
     this._dataGrid.addEventListener(WebInspector.DataGrid.Events.SelectedNode, this._onSelectionChanged, this);
     this._dataGrid.asWidget().show(this.element);
 }
 
-/**
- * @enum {symbol}
- */
+/** @enum {symbol} */
 WebInspector.TimelineStackView.Events = {
     SelectionChanged: Symbol("SelectionChanged")
 }
 
 WebInspector.TimelineStackView.prototype = {
     /**
      * @param {!Array<!WebInspector.TimelineProfileTree.Node>} stack
      * @param {!WebInspector.TimelineProfileTree.Node} selectedNode
      */
     setStack: function(stack, selectedNode)
@@ skipping 20 matching lines @@
         return selectedNode && /** @type {!WebInspector.TimelineTreeView.GridNode} */ (selectedNode)._profileNode;
     },
 
     _onSelectionChanged: function()
     {
         this.dispatchEventToListeners(WebInspector.TimelineStackView.Events.SelectionChanged);
     },
 
     __proto__: WebInspector.VBox.prototype
 }